1. Field of the Invention
The invention relates in general to elevator systems, and more specifically to elevator systems which utilize a solid state car position memory.
2. Description of the Prior Art
The operation of an elevator car is controlled by its floor selector. The floor selector keeps track of car position, and it directs the car to the correct floor to serve a call for elevator service. Certain prior art floor selectors have utilized an electromechanical device which is a scaled down version of the associated elevator system. The electromechanical device is driven in synchronism with its associated elevator car. While the electromechanical floor selector provides good results, it is costly to manufacture, and it requires considerable skill to initially set up and adjust, especially in high speed elevator systems. Also, since it is mechanical in nature, it requires periodic maintenance to keep it in proper operating condition. Thus, the trend is to replace the electromechanical floor selector with a solid state floor selector, which is more accurate, easier to install, and easier to maintain.
The solid state floor selector has many advantages over the prior art electromechanical floor selector, but it does have a disadvantage not found in the electromechanical selector. The solid state selector stores car position in a volatile memory, such as a binary counter. Loss of electrical power causes the selector to lose track of the car, and when power returns, the selector must be reset. In the solid state floor selector described in U.S. Pat. No. 3,750,850, which is assigned to the same assignee as the present application, the reset procedure involves sending the elevator car to a terminal floor, where the floor address of the terminal floor is loaded into the car position counter.
Copending application Ser. No. 775,808, filed Mar. 9, 1977 entitled "Elevator System", which application is assigned to the same assignee as the present application, sets forth a solution to the power outage problem, which solution includes the use of capacitors to store electrical energy sufficient to power the car movement detector following a power outage. Car movement following a power outage is detected and stored. When power returns, a stored indication of car movement is used to correct the car position device.
Many prior art arrangements have utilized a coded tape in the hoistway which is read by readers on the car. An improved arrangement of this type is disclosed in U.S. Pat. No. 3,963,098 which is assigned to the same assignee as the present application. In the arrangement of this patent, a digital code having a non-repeating bit pattern over any N consecutive bits is utilized. Thus, car position can be determined without moving the car if N readers are utilized; or, as described in a preferred embodiment, only four readers will determine the car position after the car has moved only N bits, which typically may be a foot, or less.
In U.S. Pat. No. 3,592,296, magnetic switches and vanes are arranged to provide a digital code to identify each floor and correct a notching type floor selector, if it is found to be out of step.
While the hereinbefore described arrangements all provide excellent results, it would be desirable to be able to determine the car position when electrical power is applied to the control circuits, such as upon start-up, and after return of electrical power following a power outage, without moving the car from a floor, or by simply moving the car to the closest floor if the car is not already at a floor when power returns. Further, it would be desirable to do this without requiring the use of a coded tape in the hoistway, and without requiring as many readers as bits in the floor address.